Boats of small size and even boats of considerable size are frequently towed along roads and highways to and from a body of water and this towing typically requires a towing vehicle and a suitable hitch for attachment to a trailer which carries the boat. Frequently the trailer is designed to be backed into the water by the towing vehicle and the boat is floated free of the trailer. Such trailers are heavy, somewhat expensive and they tend to be deteriorated with repeated submerging. Trailers also tend to cause damage to the carried boat with repeated trailering because they usually support the boat along the hull where boats are least sturdy. A number of arrangements have been taught for making it possible to load, carry, and unload small boats from the top of a car, truck or camper. Such systems are practical if the boat is not too heavy, but they normally require structure for lifting the boat up and down and also a dolly for moving the boat to the water once it is removed from the carrying vehicle. Such a design is shown in U.S. Pat. No. 3,445,018 to Reagan. Applicant's copending application Ser. No. 529,047 also shows a car top carrier design. Other special dolly and tow bar arrangements have been devised for moving a small boat for short distances by means of a towing vehicle but are not intended for high speed highway towing or for towing over rough terrain. Such structures are shown in U.S. Pat. Nos. 4,392,665 and 4,344,635 to Miller et al and Welton, respectively. None of the foregoing really deal with the problem of transporting a boat at highway speeds without requiring the lifting devices and dolly of the boat carrying arrangements or the expense and damage problems connected with repeated trailering on the usual boat trailer.